BIOSYNTHETIC INCORPORATION OF THE AMINOBUTYL GROUP OF SPERMIDINE INTOPYRROLIZIDINE ALKALOIDS

In short-term tracer experiments [H-3]putrescine and [C-14]spermidine were fed simultaneously to root cultures of Senecio vulgaris. The spec ific incorporation of the two tracers into putrescine, spermidine and pyrrolizidine alkaloids was followed over a period of 30 to 480 min. T he results show that the aminobutyl moiety of spermidine is directly i ncorporated into the necine base of pyrrolizidine alkaloids. The Same experiment carried out in the presence of the diamine oxidase inhibito r beta-hydroxyethylhydrazine, which blocks the alkaloid biosynthesis a fter homospermidine, revealed the same specific incorporation into acc umulating homospermidine. The results are in accordance with the subst rate specificity of plant homospermidine synthase (EC 2.5.1.44) which uses both putrescine and spermidine as donor for the amino butyl group . Under physiological conditions more than half of the aminobutyl moie ty of homospermidine comes directly from spermidine. This is the first report for the role of spermidine as aminobutyl donor in alkaloid bio synthesis. The importance of the linkage between spermidine and pyrrol izidine alkaloid biosynthesis is discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.